Buggy code:
public class JailIO { private JailMain pl ; private FileConfiguration flat ; private FileConfiguration records ; private Connection con ; private int storage = - 1 ; private String prefix ; private boolean changed = false ; protected JailIO ( JailMain plugin ) { } @ SuppressWarnings ( "deprecation" ) protected void loadLanguage ( ) { } protected boolean prepareStorage ( boolean doInitialCreations ) { } private Connection getConnection ( ) { } protected void closeConnection ( ) { } private void createTables ( ) { } protected void loadJails ( ) { } private void loadJailFromFlatFile ( String name ) { } protected void saveEverything ( ) { } protected void saveJail ( Jail j ) { } public void saveCell ( Jail j , Cell c , boolean force ) { } protected void removePrisoner ( Jail j , Prisoner p ) { } protected void removePrisoner ( Jail j , Cell c , Prisoner p ) { } public void removeCell ( Jail j , Cell c ) { if ( c . hasChest ( ) ) c . getChest ( ) . getInventory ( ) . clear ( ) ; if ( c . hasPrisoner ( ) ) { pl . getLogger ( ) . warning ( ( ( ( ( "Removing<seq2seq4repair_space>of<seq2seq4repair_space>cell<seq2seq4repair_space>'" + ( c . getName ( ) ) ) + "'<seq2seq4repair_space>from<seq2seq4repair_space>the<seq2seq4repair_space>jail<seq2seq4repair_space>'" ) + ( j . getName ( ) ) ) + "'<seq2seq4repair_space>failed<seq2seq4repair_space>as<seq2seq4repair_space>it<seq2seq4repair_space>has<seq2seq4repair_space>a<seq2seq4repair_space>prisoner." ) ) ; return ; } switch ( storage ) { case 1 : try { PreparedStatement p = getConnection ( ) . prepareStatement ( ( ( "delete<seq2seq4repair_space>from<seq2seq4repair_space>`" + ( prefix ) ) + "cells`<seq2seq4repair_space>where<seq2seq4repair_space>name<seq2seq4repair_space>=<seq2seq4repair_space>?<seq2seq4repair_space>and<seq2seq4repair_space>jail<seq2seq4repair_space>=<seq2seq4repair_space>?;" ) ) ; p . setString ( 1 , c . getName ( ) ) ; p . setString ( 2 , j . getName ( ) ) ; p . executeUpdate ( ) ; p . close ( ) ; } catch ( SQLException e ) { e . printStackTrace ( ) ; pl . getLogger ( ) . severe ( "----------<seq2seq4repair_space>Jail<seq2seq4repair_space>Error!!!<seq2seq4repair_space>----------" ) ; pl . getLogger ( ) . severe ( ( ( ( ( "Error<seq2seq4repair_space>while<seq2seq4repair_space>removing<seq2seq4repair_space>the<seq2seq4repair_space>cell<seq2seq4repair_space>'" + ( c . getName ( ) ) ) + "'<seq2seq4repair_space>from<seq2seq4repair_space>the<seq2seq4repair_space>Jail<seq2seq4repair_space>'" ) + ( j . getName ( ) ) ) + "',<seq2seq4repair_space>please<seq2seq4repair_space>check<seq2seq4repair_space>the<seq2seq4repair_space>error<seq2seq4repair_space>and<seq2seq4repair_space>fix<seq2seq4repair_space>what<seq2seq4repair_space>is<seq2seq4repair_space>wrong." ) ) ; } break ; case 2 : try { PreparedStatement p = getConnection ( ) . prepareStatement ( ( ( "delete<seq2seq4repair_space>from<seq2seq4repair_space>`" + ( prefix ) ) + "cells`<seq2seq4repair_space>where<seq2seq4repair_space>name<seq2seq4repair_space>=<seq2seq4repair_space>?<seq2seq4repair_space>and<seq2seq4repair_space>jail<seq2seq4repair_space>=<seq2seq4repair_space>?<seq2seq4repair_space>limit<seq2seq4repair_space>1;" ) ) ; p . setString ( 1 , c . getName ( ) ) ; p . setString ( 2 , j . getName ( ) ) ; p . executeUpdate ( ) ; p . close ( ) ; } catch ( SQLException e ) { e . printStackTrace ( ) ; pl . getLogger ( ) . severe ( "----------<seq2seq4repair_space>Jail<seq2seq4repair_space>Error!!!<seq2seq4repair_space>----------" ) ; pl . getLogger ( ) . severe ( ( ( ( ( "Error<seq2seq4repair_space>while<seq2seq4repair_space>removing<seq2seq4repair_space>the<seq2seq4repair_space>cell<seq2seq4repair_space>'" + ( c . getName ( ) ) ) + "'<seq2seq4repair_space>from<seq2seq4repair_space>the<seq2seq4repair_space>Jail<seq2seq4repair_space>'" ) + ( j . getName ( ) ) ) + "',<seq2seq4repair_space>please<seq2seq4repair_space>check<seq2seq4repair_space>the<seq2seq4repair_space>error<seq2seq4repair_space>and<seq2seq4repair_space>fix<seq2seq4repair_space>what<seq2seq4repair_space>is<seq2seq4repair_space>wrong." ) ) ; } break ; default : if ( ( flat ) != null ) { <START_BUG> flat . set ( ( ( ( "jails." + ( j . getName ( ) ) ) + "cells." ) + ( c . getName ( ) ) ) , null ) ; <END_BUG> try { flat . save ( new File ( pl . getDataFolder ( ) , "data.yml" ) ) ; } catch ( IOException e ) { e . printStackTrace ( ) ; pl . getLogger ( ) . severe ( "----------<seq2seq4repair_space>Jail<seq2seq4repair_space>Error!!!<seq2seq4repair_space>----------" ) ; pl . getLogger ( ) . severe ( ( ( ( ( "Removing<seq2seq4repair_space>of<seq2seq4repair_space>the<seq2seq4repair_space>cell<seq2seq4repair_space>'" + ( c . getName ( ) ) ) + "'<seq2seq4repair_space>from<seq2seq4repair_space>the<seq2seq4repair_space>jail<seq2seq4repair_space>'" ) + ( j . getName ( ) ) ) + "'<seq2seq4repair_space>errored<seq2seq4repair_space>out<seq2seq4repair_space>while<seq2seq4repair_space>on<seq2seq4repair_space>saving." ) ) ; } } break ; } } protected void removeJail ( Jail j ) { } public void addRecordEntry ( String uuid , String username , String jailer , String date , long time , String reason ) { } public List < String > getRecordEntries ( String username ) { } }

Fix:
flat . set ( ( ( ( "jails." + ( j . getName ( ) ) ) + ".cells." ) + ( c . getName ( ) ) ) , null ) ;